IE 7 only runs when Run As Administrator - Vista

My son's laptop has two accounts on it, his and mine, both of which are set up as administrator, when clicking on th IE icon on the desktop using my account, all works fine, but when using his account IE will not start unless you right click the icon and select Run as Administrator, when all seems to be OK. It used to work by just clicking the icon.

I've just run Avast and Ad-Aware, neither of which reported anything untoward. Spybot and Spyware Blaster are installed and up to date. I've also downloaded and ran ccleaner.

Just tried Firefox 2 on my son's account. This does run by just clicking on the icon, but will not display the home pages for click here or click here unless the icon was right clicked and started using Run as Administrator.Both sites display OK on my account when starting Firefox by just clisking the icon.